Process and plant for converting hazardous waste containing chromium VI into non-hazardous waste

Abstract

The instant invention relates to a process and plant for the transformation of dangerous wastes containing chromium six as contaminant into non dangerous wastes that can be stored without special care and will be degraded in the environment without time limit. The process basically consists of milling, extracting chromium six in liquid phase and under controlled conditions of stirring, time and temperature, proceeding then, through reduction, to transform the chromium six in chromium three and then precipitating as chromium trioxide, through gasification. The solid resulting from the transformation process can be used as raw material for the manufacturing of firebricks or eventually for the manufacturing of bricks used in the building industry through a process not included in the instant description.

The invention claimed is: 
     
       1. A process for the transformation of dangerous wastes containing chromium six into non dangerous wastes, characterized by the following steps:
 a) a first milling step wherein the dangerous waste is passed through a jaw crusher to reduce the largest pieces formed during the storage of the wastes into particles with a diameter no larger than 2.54 cm (one inch); 
 b) a second milling step wherein the particles from step (a) are passed through a ball mill to obtain a powder 
 c) a first step of washing the powder from step (b) with water to extract the chromium six in liquid phase and its soluble salts; 
 d) adding gradually to the washed powder from step (c) the residual sulfuric acid coming from liquid vaseline manufacturing to form a solution while maintaining the temperature of the solution at a level not above 80° C. and controlling the pH of the solution to be at a value of 2.5 +/−0.5; and 
 e) stirring the solution from step (d) for approximately half an hour and then injecting a gas stream of reducing agent through the solution, under constant stifling, thereby transforming dangerous wastes containing chromium six into non dangerous wastes. 
 
     
     
       2. The process according to  claim 1 , comprising the further step of unloading the milled material to separate the water from the non dangerous waste through decantation in storage cells or through filters. 
     
     
       3. The process according to  claim 1 , comprising the further step of transforming the chromium six into chromium three and then precipitating it as chromium trioxide, through gasification. 
     
     
       4. The process according to  claim 1 , comprising the further step of using the milled material obtained in the process as raw material for manufacturing bricks and/or firebricks.